@julian the next time you see this, could you open your browsers javascript console so we can see if there are any error messages displayed? I’d also be interested in a screenshot of the full dashboard to look for other visual hints as to what might be up.

I am using an ESP8266 board and have the same issue (been like this for at least 2 months) unable to delete widgets. Just get the spinning wheel. Strange thing is tho up until this week I have been able to delete the widget from within the app on my iphone but not from within a web browser.
However, now I create a widget within the web browser, I still can’t delete it from the web browser but worse, the widget never appears in the iphone app.
So its just kinda all going backwards. I have written a script to email me sensor info every few hours to get around having to deal with the Cayenne issues. I first read about the delete issue back in April, disappointing it hasn’t been resolved by now.